Heretofore, contacts between microwave coaxial connectors generally have been made by pushing on a pushrod, spring-return connected to an electrically-conductive reed or switch blade which positions the reed in a position bridging across conductive center pins of the connector. Typically the conductive parts are constructed of gold-plated beryllium copper which provides very good solderability, wear and RF qualities. Switching of the positions of a mechanical switch actuator can take place both in the power-off and power-on conditions. The pushrods can be actuated individually by actuating coils above each pushrod or a rotary drive may be used to sequence through an angular travel to depress each of the arrays of pushrods one-by-one. Single-pole-double throw (SPDT) coaxial switches have been employed to alter the path of an incoming signal to one or the other of two outputs or to select one input for an output. Particularly, current so-called T-switches for operating a 6-reed standard arrangement or array 10 of reeds shown in prior art FIG. 1 of U.S. Pat. No. 5,281,936 assigned to Applicant's assignee utilize a series of dielectric pushrods 11, each attached to a series of reeds 12a and 12b. Depression of one pushrod moves the reed 12a to electrically bridge across RF conductor contacts 14 and 15 and depression of another pushrod moves reed 12b to bridge across contacts 14 and 16, when the reeds are depressed by a force vector against a particular pushrod 11. FIG. 1 shows short reed 12a and long reed 12b in a switch open condition, while reed 12c and 12d are in a switch closed condition between contacts 14 and 17 and 15 and 16, respectively. Return springs 18 return the pushrods and reeds to their normal "unpushed" position upon release of the force vector. In the open stroke the reed is forced against the top of a housing cavity. This effectively presents a waveguide below cut off frequency.
The U.S. Pat. No. 5,281,936 discloses a random selection drive for selectively actuating one or more than one reed, e.g. two reeds, so that the reed(s) quickly, and with minimum travel and energy, bridge over a respective pair of microwave connector contacts of an array of such contacts, typically six in number. At least two actuators preferably in the form of cantilevered leaf springs, typically three in number, are mounted at different levels or parallel planes relative to the drive body. Means for displacing the leaf springs are provided, typically include a wobble plate having integral depending pusher arms of various lengths. The distal ends of the pusher arms terminate juxtaposed to a respective leaf spring in the same particular parallel neutral plane as the leaf spring. The pusher arms extend from the underside of the wobble plate facing the leaf springs. When the wobble plate is rocked by repelling or attraction forces provided by a series of spaced magnetic coils mounted on the drive body and spaced from a top side of the wobble plate, one or two of the leaf springs are displaced to push a particular reed(s) into bridging contact with a pair(s) of the array of microwave connector contacts.
FIGS. 1A, 1B and 1C of this application illustrate, respectively, the three operating portions of the prior art four port T-switch shown in U.S. Pat. No. 5,281,936 which provides two RF paths only.
The RF circuit in the prior art T-switch utilize TEM (transverse electromagnetic wave) transmission lines that have a rectangular cross section. A center-conductor is made up of rectangular transmission line sections. These sections of the transmission lines are moved, vertically, in or out of the contact with input and output connector-pins to provide the switching action. In the open state between a port and RF common the inner conductor is forced against the top of a cavity by a return spring. This effectively presents a waveguide below cutoff-frequency between these two ports. The resulting isolation for this path is a minimum of 70 Db from DC to 6 Ghz, and a minimum of 60 Db from 6 to 14 Ghz. The "closed" path between another port and RF common is maintained in contact with the connectors by a force supplied from a latching drive circuit. This path exhibits a very low insertion loss of less than 0.1 Db through 2.5 Ghz. The VSWR (voltage Standing Wave Ratio) of this path is also quite good, being typically 1.10:1 through 2.5 Ghz AND 1.30:1 through 14 Ghz.
The basic drive circuit in the prior art T-switch utilizes two coils, two magnetic iron cores, a rocker assembly, a magnetic iron support plate, and a permanent magnet. These parts are arranged in such a manner that two permanently magnetic paths are developed, namely one path for the "open" switch position, and the other for the "closed". Since the closed path is significantly stronger than the open path, the rocker will remain in a given position until acted upon by an opposing field. When a voltage pulse is applied to the coil in the closed path, the rocker is repelled and attracted by the core of the opposite coil. This latches the rocker in the opposite position. The change in rocker position activates (moves) the dielectric rods which control the vertical movement of the two inner conductors. This type of drive circuit has several advantages. The drive is extremely simple, having essentially only one moving part; the rocker. Low friction is provided by a single center-pivot point on the rocker. Efficiency is high because the contact gram-forces are maximized and the drive current is minimized. However, there has been a need to have a microwave transfer switch with more than two RF paths. This is desirable since this allows for the handling of additional signal transmission.